Flight trainers and other computer controlled simulators are currently capable of providing the illusion of traveling across a computer generated landscape. Such simulators, however, are limited by the amount of image data which can practically be presented in a real time simulation. This limitation forces a reduction from that desired in either the field of view of the simulation or the resolution of the images presented. An optimal simulation display would have a field of view of 180.degree. and a resolution of at least one minute of arc. This goal is difficult to achieve, however, because such a display would require approximately 60 million picture elements or pixels. A one thousand line television picture generates about 500,000 pixels. Thus, the equivalent of approximately 100 television monitors would be required to generate an optimum simulator display. As the total cost of such a system would be unacceptable, alternative approaches have been utilized.
One of the more promising approaches takes advantage of the nature of human vision. The eye breaks its visual field into areas of acuity, the angular resolution of which decrease as the view angle increases from the foveal axis of the eye. A 180.degree. computer generated simulator display that similarly decreased the amount of information contained in the image towards its edges, that is, reduced the number of pixels of the image in proportion to the pixels' distance from the center of the display, would be able to significantly reduce the total number of pixels needed for the display. A 180.degree. display having such a variable resolution, one matching the variable acuity of the eye, would require only approximately 200,000 pixels. This number of pixels could easily be generated by a 1,000 line TV or currently available computer systems.
Such a variable acuity display system requires a non-linear lens for the proper projection of the images onto a screen. The preferred screen for such a system is hemispherical in shape, providing a 180.degree. field of view. The focal length of a suitable non-linear lens varies by its field angle with the same function as eye acuity. Such a lens projects variable sized pixels onto the screen which provides full support of human vision. The variable sized pixels projected provide an image having a high resolution in the center of the viewing area (on the optical axis) and lower resolutions moving away from the center of the viewing area (away from the optical axes). In order to maintain the high resolution of the optical axis of the system in alignment with the foveal axis of the viewer's eye, the non-linear lens system is mechanically rotated in two axes in synchronization with the eye movements of the viewer.
Existing variable acuity non-linear lenses are comprised of multiple aspherical and simple lenses. The number and type of lenses required make current non-linear lenses are costly, difficult to manufacture and relatively heavy. The greater the weight of the lens the more difficult it becomes to rotate the lens to maintain alignment between the visual axis of the projected images and the foveal axis of the viewer's eye.
An improved variable acuity non-linear system and lens is needed, wherein the lens is lightweight, simple in form, and inexpensive to produce.